1. Field of the Invention
This invention relates generally to magnetic recording and reproducing apparatus of the type in which signals are recorded on a magnetic tape in tracks extending obliquely across the latter by means of one or more rotary heads, and more particularly is directed to improvements in such apparatus for use in the editing of video signals to be recorded or reproduced thereby, or in the still reproduction of a television picture by the repeated reproduction of a video signal recorded in one of the tracks.
2. Description of the Prior Art
In existing apparatus of the described type, during the recording of video signals in the oblique tracks on the tape by means of the rotary head or heads, control signals derived from the vertical synchronizing pulses or portions of the video signals for each field or frame of the television picture are recorded by means of a fixed head at correspondingly spaced apart locations along the tape. During the recording and reproducing operations, reference signals derived from the vertical synchronizing pulses or from the recorded control signals, respectively, are compared with reference signals indicating the rotational positions of the rotary head or heads to control the rotational speed of the latter and therby ensure that the video signals for each field or frame are properly recorded in a respective oblique track or that the oblique tracks are properly scanned by the rotary heads, respectively.
In recording video signals it may be desired to record only certain portions of the video signals being received from a suitable source, for example, for the purpose of editing the received signals or for economizing on the amount of tape being consumed. During the reception of a portion of the video signals which is not to be recorded, the driving of the tape is halted and the rotary heads are made inoperative to record that portion of the received video signals. Thereafter, when the video signals being received are again to be recorded, the driving of the tape is restarted and the heads are again made operative to record the received video signals and the control signals. Similarly, in editing recorded video signals, it may be desired to retain only certain portions of the recorded video signals and to replace another portion of the recorded signals with other video signals being received from a suitable source. In the latter case, the recorded video signal are reproduced until the end of the portion thereof to be retained, at which point driving of the tape is halted, the operation of the apparatus is switched from its reproducing mode to its recording mode and driving of the tape is restarted for recording thereon the new video signals being received.
However, when a tape is being edited, as aforesaid, with the existing apparatus of the described type, the actuation of the control switch or the like provided for halting and restarting the driving of the tape can occur at any random point in time relative to the reference or control signals which are being recorded on, or reproduced from the tape. Thus, when driving of the tape is halted, the tape can come to rest with the last recorded or reproduced track and its corresponding control signal on the tape at random positions relative to the fixed head. Similarly, when driving of the tape is restarted, the time delay between the actual commencement of movement of the tape and the occurrence of the next reference or control signal to be recorded on the tape is indeterminate. Thus, the distance along the tape between the control signals and the respective oblique record tracks that immediately precede and follow the location of a splice, that is, the junction between signals recorded before and after halting of the tape drive, may vary from the uniform or standard distance along the tape between the control signals and respective record tracks recorded during normal recording operation. As a result of the foregoing, when the signals recorded on the edited tape are reproduced, the control signals that follow the location of the splice will be out of phase relative to the control signals preceding the splice, and consequently so-called "jitter" will occur in the picture reproduced from the video signals recorded on the edited tape.
A similar problem is encountered when the existing apparatus has its tape drive halted for the still or stop motion reproduction of a television picture by the repeated scanning of the video signal recorded in one of the oblique tracks. Since the angle between the record tracks and the longitudinal axis of the tape is influenced by the 192 or movement of the tape about the guide drum during recording, it will be apparent that the rotary head or heads will scan along a line or path at an angle to the record tracks when the tape is at rest for still reproduction. Further, in order to provide a high density of video information on the tape, the spacing between adjacent oblique record tracks is desirably made very narrow. Therefore, if when the tape drive is halted for still or stop motion reproduction the head or heads scan along a line or path that cuts across the opposite end portions of two adjacent record tracks, the different signals recorded in such tracks may interfere and further so-called "drop-out" may occur at the center of the resulting picture. In order to avoid the foregoing, it is necessary that the line or path along which the head or heads scan the tape when the latter is at rest intersect the longitudinal median of an oblique record track at the middle of the latter, that is, mid-way between the ends of the oblique track. However, as previously mentioned, in the existing apparatus, the position at which the tape actually comes to rest upon the halting of the tape drive is not precisely determined with the result that the rotary head or heads may disadvantageously scan end portion of two adjacent tracks. Accordingly, it has been the practice to manually adjust the position of the tape after it has come to rest for obtaining the proper still reproduction of the video signal recorded in a single oblique track.